Meters Part 1

Meters allow gardeners to measure specific elements so each can be incrementally improved. Meters also help you find the weakest point in the chain of growth. Meters and test kits measure air, water, growing mediums, electricity, light, sound, and more. They can be analog, digital, or reagent test kits. Digital and analog meters perform hundreds of tests; reagent kit tests are limited to consumables, which must be replaced.

Meter housing should be durable and waterproof, and meters should be easily calibrated (if necessary) or self-calibrating, although some more sensitive meters with a sealed housing must be periodically returned to the factory for calibration. Other important features include: automatic temperature compensation (ATC), temperature readings in degrees Fahrenheit (oF) or degrees Celsius (oC), backlit liquid crystal display (LCD), microprocessor, memory, replaceable electrode, a broad range of accurate measurement, accuracy (+/-) listing, the ability to interface with computers or cell phones, and availability in handheld/portable or wall- or counter-mounted units with battery and instructions included. Some meters are available with remote probes at an additional cost. Some meters may have several components and wireless communication capabilities. Also note that some meters are subject to contamination and aging.

A few meters are essential—electrical circuit testers, thermometers, and hygrometers top the list. These meters will allow you to measure air temperature and humidity (moisture) content. Thermometers can also measure the temperatures of soils and nutrient solutions. The next most essential meters include pH and electrical conductivity (EC) meters, which measure parts per million (ppm) and total dissolved solids (TDS). More expensive models of these meters will take measurements perpetually and store a record that can be uploaded to a computer, mobile telephone, or Internet site. (It is easy to set up a security camera and monitor it with an iPhone, iPad, Android telephone, or computer. The data can then be analyzed and acted upon. However, many medical cannabis gardeners prefer not to send such delicate information by telephone.)

The Garden Meters table shows recommended meters for “Basic” and “Advanced” gardens. Use this information only as a guideline. The prices are approximate and may vary from country to country. Prices are approximate.

To see more than 1,800 scientific videos on how to master any meter that you could possibly imagine, type “MIT Digital Lab Techniques Manual” into a web browser. Click on the YouTube link to go to the Massachusetts Institute of Technology’s videos.

You can also type “video digital (name/type of) meter” into Google and see numerous videos on how to calibrate and use specific meters.

It can be difficult to find all the meters you want at one store. I had to go to the auto parts store to buy a digital laser thermometer, for example, rather than a gardening center. Find, research and order any meter you need by typing in “buy (name of meter)” into a web browser.

Air Meters

Anemometers measure air or wind speed. They are common weather station instruments. There are two classes of anemometers; one measures wind speed and the other measures wind pressure, both of which are related. Anemometers designed for one will give information about both. Handheld meters work well to measure wind outdoors in microclimates.

I use my anemometer to measure wind around my outdoor garden. Indoors, I use it to measure air speed when setting up ventilation and circulation fans. Move it around the garden and see just how bad airflow is in between plants!

Electrochemical carbon dioxide (CO2) sensors measure electrical conductivity of an air sample in either an alkali solution or distilled/deionized water. These systems are relatively inexpensive, but they have drawbacks: limited accuracy and sensitivity to temperature and air pollutants. Most CO2 sensors or meters are nondispersive infrared (gas) sensors (NDIR) and chemical gas sensors.

These sensors are used in the air conditioning, horticulture, building, and safety industries to monitor air quality and CO2 levels. NDIR sensors measure infrared radiation emitted from a heated surface. Most devices can measure from 0 to 5,000 ppm CO2. Set up sensors in the garden room or in air ducts. CO2 sensor/controllers will turn compressed CO2 and generators on and off at desired levels. More sophisticated CO2 controllers can be synchronized with controllers that operate heat, ventilation, and CO2 generators. Shop around to find sensors that are battery or AC-powered and wall mounted with remote probes.

Disposable comparative colorimetric CO2 test kits are fairly easy to use and inexpensive. CO2 detector tubes are used to make spot tests.

Hygrometers measure relative humidity (RH)—moisture content in the air at a given temperature. Most hygrometers convert measurements of temperature, pressure, mass, or an electrical or mechanical change in a material as it absorbs moisture. Humidity is difficult to measure accurately. Hygrometers are available in three basic types: metal/pulp coil, hair tension, and electronic. I cannot recommend metal/pulp coil types because their accuracy is limited. Hair tension hygrometers use human or animal hair under tension that changes length as humidity changes. Hair tension hygrometers are more accurate, but still not as accurate as electronic versions.

Electronic chilled mirror dew point

hygrometers give precise measurements—as accurate as } 0.5 percent RH when clean and calibrated.
Capacitive humidity sensors are pretty accurate (} 2%) and are little affected by condensation and high temperatures over short periods.
Resistive humidity sensors measure electrical resistance relative to humidity. Meters with capacitive sensors are more sensitive than those with resistive sensors. Resistive humidity sensors usually have an accuracy rating of } 3 percent.
Thermal conductivity humidity sensors measure absolute humidity.
A humidistat is a hygrometer with a control feature.
A psychrometer also measures relative humidity. It has 2 bulbs: 1 dry and 1 wet. Water on the wet bulb evaporates and the temperature of each bulb is measured. The difference between temperatures is logged and correlated on a chart to find the relative humidity. A psychrometer can also be used to measure dew point and make basic weather predictions.

Thermometers measure temperature. Many people prefer old reliable liquid-and-glass thermometers with a Fahrenheit scale on one side and a Celsius scale on the other. Inexpensive spring-type thermometers are not accurate enough for medical cannabis gardeners. I prefer digital thermometers that record both indoor and outdoor temperatures. They also have a maximum and minimum readout that can be reset. More expensive thermometers record daily data and store it for downloading to a computer.

Digital laser thermometers are a lot of fun and incredibly informative to use. The thermometer projects a laser beam and records the temperature at the end of the beam. I use mine to measure leaf and stem surface temperatures, and those of water, soil, and walls—any temperature, really. Accurate temperature readings come in very handy when solving culture issues or pest and problems. Always take temperature readings at different points in the room.

A thermostat measures temperature and perpetually controls heating and cooling devices such as heaters, fans, and air conditioners.

Smoke detectors detect smoke. Some detectors are connected to a fire alarm. Inexpensive and readily available battery-powered smoke detectors should be placed at high points in garden rooms, where smoke will collect. Most of these devices detect smoke by optical detection (photoelectric) or by ionization. More expensive models use both detection methods. Automatic fire extinguishers come with a built-in smoke detector. Mount handheld fire extinguishers by exit and entrance doors so you will know where they are when a room you are in fills with smoke.

Carbon monoxide (CO) detectors

identify the presence of deadly CO gas, to prevent carbon monoxide poisoning. A product of incomplete combustion, colorless odorless CO, the “silent killer,” is virtually undetectable without a CO detector. Elevated levels of CO are dangerous to humans, and low concentrations can be harmful over time. Use a CO detector to guard against high levels of CO if using a kerosene or fossil fuel CO3 generator or internal combustion motor.
Note: It can take up to a year for CO to release from the blood. CO accumulates over time!

This is the first part of an excerpt from chapter 15, “Meters” from the Cannabis Encyclopedia (596 pages, 2,000+ color images, large A4 format) by Jorge Cervantes, available on amazon. For more information please see Jorge´s website, www.marijuanagrowing.com.